The diktat was, once you get 12 reps, increase weight (5 lbs). Consider a case where you are using 150 lbs, but actually have the capacity to get in 160 lbs for the target reps. You would increase the weight next workout to 155

This is the approach I used for a very long time. My focus was always on adding reps, as opposed to adding weight each week. Once I hit the target rep ceiling I added weight. This is also the method I primarily teach, though it's not exactly like the Reeves approach.